The present invention relates to a bail lock for coverings for architectural openings, such a blinds or shades. More particularly it relates to a bail lock which has different zones of operation wherein the amount of friction applied to the cord varies across the width of the lock.
Typically, a blind transport system will have a head rail which both supports the blind and hides the mechanisms used to raise and lower or open and close the blind. One blind system is described in U.S. Pat. No. 6,536,503, Modular Transport System for Coverings for Architectural Openings (the '503 patent), which is hereby incorporated herein by reference. In the typical top/down product, the raising and lowering of the blind is done by a lift cord or lift cords suspended from the head rail and attached to the bottom rail (also referred to as the moving rail or bottom slat). The opening and closing of the blind is typically accomplished with ladder tapes (and/or tilt cables) which run along the front and back of the stack of slats. The lift cords usually run along the front and back of the stack of slats or through holes in the middle of the slats. In these types of blinds, the force required to raise the blind is at a minimum when the blind is fully lowered (fully extended), since the weight of the slats is supported by the ladder tape so that only the bottom rail is being raised at the outset. As the blind is raised further, the slats stack up onto the bottom rail, transferring the weight of the slats from the ladder tape to the lift cords, so progressively greater lifting force is required to raise the blind as the blind approaches the fully raised (fully retracted) position. As the blind is raised and the lifting force increases, the holding force that must be applied to the cord in order to hold the blind in place also increases. This is also the case for most shades and other coverings in which a lift cord is used.
Typically, the lift cord is held in a fixed position by means of a bail lock or some other friction mechanism, which applies sufficient frictional force to the cord to prevent the blind from falling when the cord is released. A conventional bail lock grabs the cord anywhere across its width, as shown in FIGS. 19, 20, and 21. In the prior art, the cord that is grabbed by the bail lock usually is the lift cord itself. However, the '503 patent shows an arrangement in which a separate drive cord drives spools onto which the lift cords wrap for raising and lowering the covering, so the cord that is pulled by the user is not the actual lift cord but is a separate cord that drives the lifting mechanism. In that case, the bail lock would be grabbing the drive cord rather than the lift cord(s), but the drive cord also is operatively connected to the covering in order to extend and retract the covering. Regardless of which cord it is grabbing, the bail lock is typically made of steel and has relatively sharp edges which tend to abrade the cord. This situation is compounded when there are fewer cords of the same cross section present with the same total load, with the most fraying of the cord occurring when there is only a single cord passing through the bail lock.